This invention relates to dispersing agents for pigments or extenders based on acrylic acid alkyl ester polymers, wherein at least part of the ester groups of the polymers are reacted to form acid amides, and to a process for producing dispersing agents of this type. The invention also relates to the use of the dispersing agents for the production of pigment concentrates and coatings.
According to the prior art, polyacrylic acid esters comprising acidic and basic groups, which can also be converted into salts, are used as dispersing agents. These are produced by the polymerisation of corresponding monomeric acrylic acid esters, such as ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, 2-hydroxyethyl acrylate and alkoxylation products thereof, and of acrylic acid and dimethylaminoethyl acrylate, for example. For these polymers, other monomers comprising vinyl double bonds can also be used in conjunction during polymerisation, such as styrene, vinylpyridine, vinylimidazole and alkyl vinyl ethers for example (EP 0 311 157, U.S. Pat. No. 3,980,602).
However, proposals have also been made regarding how dispersing agents such as these can be produced by a transesterification reaction of polyacrylic acid esters, whereby the alkyl group is replaced by longer chain, saturated or unsaturated alcohols, polyoxyalkylene monoalcohols or dialkylaminoalkanols (EP 0 595 129, DEP 3 906 702, DEP 3 842 201, DEP3 842 202).
The advantage of transesterification is stated to be the considerably narrower molecular weight distribution of polymers produced in this manner, compared with polymers produced by the polymerisation of monomers. Moreover, it is claimed that these polymers are free from interfering and toxic monomer fractions.
These products according to the prior art have the disadvantage that defined monomers which are particularly suitable for producing these polymers with a heterocyclic structure, for example, are not available commercially.
Secondly, it has been shown that the basic transesterification products described in EP 0 595 129 do not impart a satisfactory stability to dispersed pigments, i.e. the pigments flocculate again after dispersion and do not exhibit the optimum transparency and gloss development.
It is an object of the present invention to provide polyacrylic acid compounds which do not have the above disadvantages or only to a substantially lesser extent and to enable achieving a broad variety of polyacrylic acid compounds.
In this manner, acrylic acid ester/N-alkylacrylic acid amide copolymers can be obtained, the acrylic acid amides of which are not commercially available as monomers.
Surprisingly, it has been shown that significant improvements in the dispersing and stabilising effect can be achieved for acrylate polymers such as these, which are produced by a polymer analogous reaction, if the corresponding amines are used, at least in part, instead of alcohols during the reaction of the alkyl acrylates.
With suitable catalysts, such as paratoluenesulphonic acid or H2SO4 for example, aminolysis of the ester bond proceeds similarly to transesterification, with elimination of the alkanol from the polyalkyl acrylate.
In contrast, the aminolysis of acrylic acid/acrylic acid ester copolymers proceeds without further addition of a catalyst, since the carboxyl groups themselves are already catalytically active.
The object of the present invention is achieved by the provision of dispersing agents for pigments or extenders which are based on acrylic acid alkyl ester polymers, in which at least part of the ester groups of the polymer is reacted to form acid amides, wherein the dispersing agent is obtainable by the aminolysis of ester groups of the polymers by means of amines, wherein, for the aminolysis, at least one amine can be used from the group comprising a) amines of general formula NH2xe2x80x94R1xe2x80x94NR2R3, wherein R1 is a divalent alkylene radical comprising 2-4 carbon atoms and R2 and R3 are aliphatic and/or alicyclic alkyl radicals which comprise 1-12, preferably 1-6 carbon atoms and which can be the same or different, and b) amines of general formula NH2xe2x80x94R1xe2x80x94Z, wherein R1 is a divalent alkylene radical comprising 2-4 carbon atoms and Z is a 5- or 6-membered N-containing heterocycle which can comprise up to 2 nitrogen atoms or which can additionally comprise oxygen.
In addition to these amines, one or more amines can also be used from the group comprising c) saturated or unsaturated aliphatic amines comprising 6-22 carbon atoms, d) alicyclic amines comprising up to 6 carbon atoms, e) aryl-substituted alkylamines and f) polyoxyalkylene amines NH2xe2x80x94R1xe2x80x94[Oxe2x80x94R2xe2x80x94]xOxe2x80x94R3, wherein R1 is a divalent alkylene radical comprising 2-3 carbon atoms, R2 is a divalent alkylene radical comprising 2-4 carbon atoms and R3 is an alkyl radical comprising 1-4 carbon atoms.
The acrylic acid alkyl ester polymers may contain, as a comonomer, one or more monomers from the group comprising itaconic acid esters, maleic acid esters, methacrylic acid esters, (meth)acrylic acid, styrene, alkyl vinyl ethers, vinyl acetate or mixtures thereof, and preferably have a weight average molecular weight of 1000-50,000. At lower molecular weights, the acrylic acid ester polymers loose some efficiency; at higher molecular weights their processability decreases considerably due to higher viscosities. The acrylic acid alkyl ester polymers most preferably have a molecular weight of 2000 to 20,000.
The dispersing agents can also be used in the form of salts of the amino-functional polymers produced by aminolysis with a) and/or b). Phosphoric acid or phosphoric acid esters and/or sulphonic acids and/or carboxylic acids are suitable for salt formation.
Components a) and/or b) and optionally c) to f) are used in amounts such that preferably 1 to 50%, more preferably 5 to 40% and most preferably 10 to 30% of the groups which are capable of amidisation are reacted.
Aliphatic diamines comprising a tertiary amino group and a primary or secondary amino group, such as 2-(diethylamino)ethylamine, 3-(dimethylamino)propylamine, 3-(diethylamino)propylamine or 1-diethylamino-4-aminopentane for example, are used as component a) in the polyacrylates to be used according to the invention. A particularly preferred component a) is NH2xe2x80x94(CH2)3xe2x80x94N(CH3)2(dimethyl-aminopropylamine).
Heterocyclic amines comprising an additional exocyclic primary or secondary amino group, such as N-(3-aminopropyl)imidazole, N-(3-aminopropyl)morpholine or N-(2-aminoethyl)-piperidine for example, are used as components b). A particularly preferred component b) is N-(3-aminopropyl)imidazole.
Components a) and b) can be used on their own or jointly in any desired ratio.
In addition, components c)-f) can be used on their own or in admixture for the polymer analogous reaction.
2-ethylhexylamine, oleylamine or stearylamine can be used as component c) for example; cyclohexylamine or dicyclohexylamine can be used as component d) for example; benzylamine can be used as component e) for example; the polyoxyalkylene amines which are known by trade name Jeffamin(copyright) can be used as component f) for example.
In this respect, it does not matter whether the amines are reacted as a mixture or successively in several steps.
In addition, alcohols can also be incorporated by transesterification into the polymers according to the invention during aminolysis with the amines described in a)-f). This is advantageous if solubility and/or compatibility problems arise at high degrees of conversion of the ester groups with the amines listed under a)-f) to form the corresponding amides. In situations such as these, the remaining (C1-C4) alkyl ester groups can be replaced by longer chain substituents, such as oleyl alcohol, stearyl alcohol or benzyl alcohol for example, by transesterification.
Aminolysis of the polyacrylic acid esters proceeds in the manner known in the art, in the presence of catalysts, such as p-toluenesulphonic acid or H2SO4 for example, at reaction temperatures of about 130-210xc2x0 C., optionally in the presence of a suitable solvent. The alcohol which is evolved in the course of this procedure can be distilled off, during the reaction or after the reaction is complete, according to choice, or can remain in the reaction mixture.
The dispersing agents according to the invention normally used in an amount of 0.5 to 100, preferably 10 to 75, most preferably 25-60 parts by weight, with respect to 100 parts by weight of the solid to be dispersed. However, this depends on the surface area of the solid to be dispersed which is to be covered. For example, carbon black requires higher amounts of dispersing agents than does TiO2. 100 parts by weight can also be exceeded in this respect. The dispersing agents are generally deposited on the solids in the presence of organic solvents and/or water. However, they can also be deposited directly on the solids to be dispersed.
The solids which can be used are the organic and inorganic pigments which are known to one skilled in the art, and which are listed both in the Pigment Handbook, Vol. 1-3, John Wiley and Sons, New York 1988 and in Ullmann""s Encyclopedia of Industrial Chemistry, 5th Edition, Vol. 20, pp. 213 et seq. (Phthalocyanines) and pp. 371 et seq. (Pigments, Organic). Carbon black, TiO2, iron oxide pigments, phthalocyanines and azo pigments can be cited as examples here. Moreover, mineral extenders, e.g. calcium carbonate or calcium oxide, and also flame retardants, such as aluminium or magnesium hydroxide for example, can be dispersed. Matting agents, such as hydrated silicas for example, can also be dispersed and stabilised in an outstanding manner. Other examples are described in EP 0 318 999, for example.
The dispersing agents according to the invention are particularly suitable for the production of pigment concentrates. For this purpose, the compounds according to the invention are introduced into an organic solvent and/or water, and the pigments to be dispersed are added with stirring. In addition, these pigment concentrates may contain binder vehicles and/or other adjuvant substances. These pigment concentrates can be incorporated in various binder vehicles, such as alkyd resins, polyester resins, acrylate resins, polyurethane resins or epoxy resins for example. However, pigments can also be dispersed directly, solvent free, in the polyacrylates according to the invention, and are then particularly suitable for the pigmentation of thermoplastic and thermosetting plastics formulations.
The dispersing agents according to the invention are particularly suitable for the production of coatings, wherein a binder vehicle, optionally a solvent, pigments and/or extenders, the dispersing agent and optionally adjuvant substances are dispersed together.